The invention relates to a self-crosslinking heat-curable binder, in particular for electropaints, which is based on an organic synthetic resin which contains primary and/or secondary and, if desired, also tertiary amino groups and esterified carboxyl groups and is water-dilutable due to partial or complete neutralization with acids.
German Offenlegungsschrift No. 2,936,411, corresponding to U.S. Pat. No. 4,373,072 discloses a coating agent which contains a synthetic resin which contains primary and/or secondary and, if desired, also tertiary amino groups and terminal esterified carboxyl groups which are largely stable in a neutral aqueous medium but are reactive in a basic medium at elevated temperatures to the primary and/or secondary amino groups of the synthetic resin. According to the example of German Offenlegungsschrift No. 2,936,411, baking is carried out at 180.degree. C. for 25 minutes.
In this known synthetic resin, only those monoalcohols are used as the alcohol component of the carboxylate groups which contain 1 to 18, preferably 1 to 6, carbon atoms in the molecule. Low-boiling alcohols which have a boiling point of less than 140.degree. C. are particularly preferred. The reactivity of the esters is increased by increasing the electrohphilic activity of the carboxyl group. It is said that the incorporation of methyl, ethyl and/or propyl esters of lactic acid or dimethylolpropionic acid is particularly suitable. The use of monoalcohols as the esterification component has the disadvantage that the resulting carboxylate groups are not sufficiently reactive despite their activation in the carboxylic acid component.